Various techniques have been proposed, which can increase the weight of footwear if necessary to enhance the exercise effect of a wearer while keeping the weight decreased at normal times.
An example of such techniques is disclosed in Korean Registered Utility Model Serial No. 285242, entitled “Sports Shoes for Exercise”. According to this document, heavy metal members are detachably inserted into an outsole or a bottomsole as the outer bottom portion of the footwear in order to enhance the exercise effect of a wearer.
Another example is disclosed in Korean Registered Utility Model Serial No. 298008, entitled “Weight Adjustable Footwear Liner”, proposed by the inventor. This document proposed insertion of metal members into an insole or liner, which is put in a footwear body, to increase the weight of the footwear thereby enhancing the exercise effect of a wearer.
According to the conventional techniques, high specific gravity material such as metal, which is inserted into the outsole or the insole for increasing the weight of shoes, lowers the shoes' ability of absorbing the load impact applied to a wearer thereby requiring additional shock-absorbing means.
Because additional molds as well as fabrication and assembly processes are necessary in order to provide a detachable structure for the weight-increasing insert members, the prior arts have another drawback that increases fabrication time and cost.
The insert members made of metal cause inconvenience to a person in the above footwear or shoes that he/she should take off the shoes or separate the metal members from the shoes when passing through an airport scanner.
Also, the shoes may be soiled from the rust of the metal members when water-washed in a washing machine.
Furthermore, if the shoes are used for a predetermined time period, the rubber outsoles are abraded, exposing the metal members, which, in turn, collide against the ground, creating unpleasant noises.
Therefore, there is a need for novel means that can overcome the foregoing problems while adjusting the weight of shoes.